Cathode configuration, cathode block with a groove, and production method

ABSTRACT

A cathode configuration for an aluminum electrolysis cell has at least one cathode block based on carbon and/or graphite. At least one groove is formed in the cathode block and the groove is lined with a graphite foil, at least in certain regions. At least one busbar is disposed in the groove and has an encasement of cast iron at least in certain regions. At least one recess is formed in the wall of the cathode block that delimits the at least one groove, and the encasement of cast iron engages into the at least one recess, at least in certain portions. A cathode block for such a cathode configuration is provided and also a process for producing a cathode configuration for an aluminum electrolysis cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, under 35 U.S.C. §120, of copendinginternational application No. PCT/EP2012/051979, filed Feb. 6, 2012,which designated the United States; this application also claims thepriority, under 35 U.S.C. §119, of German patent application No. DE 102011 004 009.9, filed Feb. 11, 2011; the prior applications are herewithincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cathode configuration for an aluminumelectrolysis cell, to a cathode block for such a cathode configurationand to a process for producing such a cathode configuration.

Electrolysis cells of this kind are used for the electrolytic productionof aluminum, which is customarily carried out in industry by way of theHall-Héroult process. In the Hall-Héroult process, a melt composed ofaluminum oxide and cryolite is electrolyzed. Here, the cryolite,Na₃[AlF₆], serves to lower the melting point of 2045° C. of purealuminum oxide to about 950° C. for a mixture containing cryolite,aluminum oxide and additives, such as aluminum fluoride and calciumfluoride.

The electrolysis cell used in this process has a bottom, which iscomposed of a multiplicity of adjoining cathode blocks forming thecathode. In order to withstand the thermal and chemical conditions thatprevail during operation of the cell, the cathode blocks are customarilycomposed of a carbon-containing material. The undersides of each of thecathode blocks are provided with grooves, in each of which there isarranged at least one busbar through which the current fed via theanodes is discharged. In this case, the interstices between theindividual walls of the cathode blocks, which delimit the grooves, andthe busbars are often sealed with cast iron, in order to electricallyand mechanically connect the busbars to the cathode blocks by virtue ofthe resulting encasement of the busbars with cast iron. An anode formedfrom individual anode blocks is arranged about 3 to 5 cm above the layerof molten aluminum located on the top side of the cathode, and theelectrolyte, i.e. the melt containing aluminum oxide and cryolite, islocated between said anode and the surface of the aluminum. During theelectrolysis carried out at about 1000° C., the aluminum which hasformed settles beneath the electrolyte layer, i.e. as an intermediatelayer between the top side of the cathode blocks and the electrolytelayer, on account of the fact that its density is relatively largecompared to that of the electrolyte. During the electrolysis, thealuminum oxide dissolved in the cryolite melt is cleaved to formaluminum and oxygen by a flow of electric current. In terms ofelectrochemistry, the layer of molten aluminum is the actual cathode,since aluminum ions are reduced to elemental aluminum on the surfacethereof. Nevertheless, hereinbelow the term “cathode” will not beunderstood to mean the cathode from an electrochemical point of view,i.e. the layer of molten aluminum, but rather the component which formsthe electrolysis cell bottom and is composed of one or more cathodeblocks.

A significant disadvantage of the cathode configurations used in theHall-Héroult process is their relatively low wear resistance, whichmanifests itself by erosion of the cathode block surfaces duringelectrolysis. In this case, on account of an inhomogeneous currentdistribution within the cathode blocks, the cathode block surfaces arenot eroded uniformly over the length of the cathode blocks, but ratherto an increased extent at the cathode block ends, and therefore thesurfaces of the cathode blocks change to a W-shaped profile aftercertain electrolysis duration. As a result of the nonuniform erosion ofthe cathode block surfaces, the useful life of the cathode blocks islimited by the areas with the greatest erosion.

In order to counter this problem, commonly assigned U.S. Pat No.7,776,191 B2 and its counterpart WO 2007/118510 A2 describe a cathodeblock with a groove which is intended for receiving a busbar and has agreater depth in the center than at the cathode block ends, with respectto the cathode block length. This achieves a substantially homogeneousvertical current distribution over the cathode block length duringoperation of the electrolysis cell, as a result of which the increasedwear on the cathode block ends is reduced and thus the service life ofthe cathode is increased.

A further disadvantage of the cathode configuration used in theHall-Héroult process is its comparatively high electrical resistance.One of several reasons for the comparatively high electrical resistanceis that the contact resistance between the busbars and the cathodeblocks of the cathode is comparatively high and this contact resistanceadditionally increases as the operating time of the cathode increases.This is caused firstly by the fact that constituents of the meltundesirably diffuse into the cathode blocks during electrolysis, whichleads to the formation of insulating layers of for example β-aluminumoxide, and secondly by the fact that the steel of the busbars, the castiron and the carbon of the cathode blocks start to creep afterrelatively long loading, i.e. the steel of the busbars, the cast ironand the carbon of the cathode blocks deform irreversibly afterrelatively long loading.

In order to reduce the electrical contact resistance between the busbarsand the cathode blocks, and therefore to increase the energy efficiencyof the electrolysis process, it has been proposed in commonly assignedU.S. Pat. No. 7,776,190 B2 and its counterpart WO 2007/071392 A2 to linethe groove of a carbon-based or graphite-based cathode block with agraphite foil at least in certain regions. Aside from the fact that thegraphite foil reduces the electrical contact resistance between thebusbar, or the layer of solidified cast iron encasing it, and thecathode block on account of its good positive fit on both sides, theelasticity of the graphite foil means that the latter also reduces inparticular the increase in this contact resistance as the operating timeof the cathode increases, because the graphite foil fills the gaps whichform during creep of the steel of the busbar and of the carbon of thecathode block between the walls which delimit the groove of the cathodeblock and the busbar.

However, graphite foils have a smooth surface with very good slidingproperties. In the case of a cathode block having a groove lined with agraphite foil, there is therefore the risk that the busbar accommodatedtherein, which usually has a length of several meters and a weight ofseveral hundred kilograms, will subsequently be displaced in the groovein an uncontrolled manner in the depth direction of the groove opening,or will even fall out of the groove, if for example the cathode block israised as it is being installed or is moved for another reason. Thisrisk is present in particular in the case of a groove having arectangular cross section, which is virtually the only applicable formfor the groove of a cathode block with a groove depth which varies overits length. In addition, the precisely fitting contact between thegroove and the cast iron is lost as a result of the busbar slipping inthe groove, and this leads to poorer current transfer from the busbar tothe cathode block and therefore to a decrease in energy efficiency.Finally, graphite foil cannot be connected to cast iron or can beconnected to cast iron only to a very small degree, and therefore thefilling of the gap between the busbar and the graphite foil by pouringliquid cast iron into it and subsequent hardening or solidification ofthe cast iron do not result in a connection between the graphite foiland the cast iron, but rather only in the busbar being encased with castiron.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

It is accordingly an object of the invention to provide a cathodeconfiguration for an aluminum electrolysis cell which overcomes theabove-mentioned disadvantages of the heretofore-known devices andmethods of this general type and which provides for an electrolysiscell, which has a low electrical resistance, which is also in particularpermanently low over an extended electrolysis period, and in particularalso a low contact resistance between the busbar and the cathode block,and in which undesirable subsequent displacement of the busbar in thegroove of the cathode block perpendicularly to the longitudinaldirection of the cathode block, i.e. in the depth direction of thegroove, and in particular falling out of the busbar from the groove isreliably prevented, to be precise in particular even in the case of agroove with a rectangular cross section, as is conventionally used incathode blocks with a groove depth which varies over the cathode blocklength.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a cathode configuration for an aluminumelectrolysis cell, the cathode configuration comprising:

at least one cathode block based on at least one material selected fromthe group consisting of carbon and graphite;

the at least one cathode block having a groove formed therein lined witha graphite foil at least in certain regions thereof;

a wall of the cathode block delimiting the groove having at least onerecess formed therein;

a busbar disposed in the groove, the busbar having an encasement of castiron at least in certain regions thereof, the encasement of cast ironengaging into the at least one recess in the groove, at least in certainportions thereof.

In other words, the objects of the invention are solved by a cathodeconfiguration for an aluminum electrolysis cell having at least onecathode block based on carbon and/or graphite, which has at least onegroove lined with a graphite foil at least in certain regions, whereinat least one busbar is provided in the at least one groove and has anencasement of cast iron at least in certain regions, wherein at leastone recess is provided in the wall of the cathode block which delimitsthe at least one groove, and the encasement of cast iron engages intothe at least one recess at least in certain portions.

This solution is based on the realization that a precisely fittingpositively-locking connection which is resistant to displacement in thedirection perpendicular to the longitudinal direction of the cathodeblock is achieved between a busbar and a cathode block having a groovelined with graphite foil if at least one recess is provided in at leastone wall of the cathode block which delimits the groove and a busbarencased with cast iron at least in certain regions is introduced intothe groove such that the encasement of cast iron engages into the recessat least in certain portions. According to the invention, it has beenidentified that, independently of the high sliding properties of thegraphite foil used, this achieves a fixed mechanical connection betweenthe busbar encased with cast iron and the cathode block perpendicular tothe longitudinal direction of the cathode block, which counteractsundesirable displacement of the busbar in this direction and inparticular falling out of the busbar from the groove lined with graphitefoil, to be precise in particular even in the case of a groove having arectangular cross section, as is preferred for cathode blocks with agroove depth which varies over the cathode block length. Therefore, thecathode configuration according to the invention has the advantage,associated with the lining of the groove with graphite foil on accountof the electrical and mechanical properties of graphite foil, ofimproved current transfer between the busbar and the cathode block andtherefore improved energy efficiency, and at the same time avoids thedisadvantage, associated with the high sliding properties of graphite,of uncontrolled mobility of the busbar in the groove in the directionperpendicular to the longitudinal direction of the cathode block andaccompanying possible impairment of the electrical connection betweenthe busbar and the cathode block in the event that the electrolysis cellis operated for a relatively long time.

In addition, the present invention makes it possible to utilize thesliding properties of the graphite foil in a targeted manner to ensurethat the busbar can be displaced longitudinally in the grooveselectively, specifically in the case of movements caused by a change intemperature during start up.

In addition, the cathode configuration according to the invention havingthe above-described advantages can be produced with extremely lowexpenditure and without complicated additional process steps. Thus, themechanical connection which is provided between the busbar and thecathode block can be achieved simply by filling a recess of the cathodeblock at least partially with the cast iron during the already requiredcasting of the busbar with the cast iron. This achieves very closecontact between the busbar, the encasement of cast iron, the graphitefoil and the cathode block, contributing to a particularly lowelectrical contact resistance between the busbar and the cathode block.In addition, the graphite foil absorbs the mechanical pressure whicharises during operation of the cathode configuration perpendicularly tothe plane of the foil.

Within the context of the present invention, in demarcation relative toa mere surface roughness, a “recess” is understood to mean a cutoutwhich, based on the surface of the wall which delimits the groove, has adepth of at least 0.05 mm and preferably of 0.5 mm.

In addition, within the context of the present invention, a “graphitefoil” is understood to mean not only thin graphite sheet, but also inparticular a partially compressed blank or a flexible plate of expandedgraphite.

Within the context of the present invention, a “cathode configuration”is understood to mean a cathode block having at least one groove,wherein at least one busbar, possibly encased by cast iron, is receivedin each of the at least one groove. Similarly, this term denotes anarrangement of a plurality of cathode blocks each having at least onegroove, wherein at least one busbar, possibly encased by cast iron, isreceived in each of the at least one groove.

In principle, the encasement of cast iron can be in direct contact withthe graphite foil or with the cathode block itself at least in theregion of the recess. Although this is preferred according to thepresent invention, it is not absolutely necessary. What in fact mattersprimarily for producing the desired mechanical connection between thebusbar and the cathode block is the fact that the encasement of castiron engages into the at least one recess at least in certain portions,i.e. fills the hollow space formed by the at least one recess at leastin certain regions.

According to a preferred embodiment of the present invention, thatportion of the encasement of cast iron which engages into the at leastone recess is configured complementarily to the recess. This makes itpossible to achieve a particularly good positively-locking engagement ofthe encasement of cast iron into the recess and therefore particularlyeffective mechanical fastening of the cast iron encasement and thebusbar connected thereto to the cathode block.

In order to achieve a particularly good positive fit between the castiron encasement and the cathode block, it is proposed in a developmentof the concept of the invention that that portion of the encasementwhich engages into the at least one recess and, if appropriate, thebusbar encased thereby fill at least 70%, preferably at least 80%,particularly preferably at least 90%, very particularly preferably atleast 95% and most preferably 100% of the recess. It is thereby possibleto particularly reliably avoid undesirable displacement of the busbar inthe direction perpendicular to the longitudinal direction of the cathodeblock and in particular falling out of the busbar from the groove.

It is advantageous that each of the at least one recess extendscontinuously over at least 20%, preferably over at least 40%,particularly preferably over at least 60%, very particularly preferablyover at least 80% and most preferably at least approximately over theentire length of the groove. This can prevent the busbar from possiblyslipping out of the groove during assembly. In addition, if the recessextends over a considerable part of the groove length, as describedabove, it is possible to ensure good displaceability of the busbar inthe longitudinal direction of the groove, in which case undesirabledisplacement of the busbar parallel to the depth direction of the grooveis still reliably prevented.

In principle, the cathode block can also have a multiplicity of recesseswhich follow one another in the longitudinal direction of the groove andare separated from one another by recess-free portions of the groove.This embodiment is particularly advantageous when longitudinaldisplaceability of the busbar in the cathode block is not desirable.

In order to ensure that the cast iron encasement and the busbar areanchored reliably in the cathode block, the at least one recesspreferably has a depth of 2 mm to 40 mm, particularly preferably of 5 mmto 30 mm and very particularly preferably of 10 mm to 20 mm.

For the same reason, the at least one recess preferably has an openingwidth, based on the height of the cathode block, of 2 mm to 40 mm,particularly preferably of 5 mm to 30 mm and very particularlypreferably of 10 mm to 20 mm.

As a consequence, the at least one recess preferably has across-sectional area of 1.5 mm² to 1600 mm², particularly preferably of10 mm² to 900 mm² and very particularly preferably of 40 mm² to 400 mm². These values are preferred in particular for recesses having apolygonal cross section and particularly having a rectangular crosssection. If the at least one recess has a curved cross section, such asfor example a substantially semicircular cross section, the at least onerecess preferably has a cross-sectional area of 1.5 mm² to 630 mm²,particularly preferably of 10 mm² to 350 mm² and very particularlypreferably of 40 mm to 160 mm².

In principle, the at least one recess can have any polygonal or bentcross section. Good results in terms of a good positively-lockingengagement of the cast iron encasement into the at least one recess andat the same time in terms of reliable and unproblematic fillability ofthe recess with cast iron during casting are achieved in particular ifthe at least one recess has an at least substantially semi-circular,triangular, rectangular or trapezoidal cross section.

In a development of the concept of the invention, it is proposed thatthe at least one recess extends substantially perpendicularly into thewall of the cathode block which delimits the groove. This brings about aparticularly reliable fixing action in the depth direction of thegroove.

According to the present invention—as considered in the depth directionof the groove—the at least one recess is delimited at each of its endsby a transition region between the recess and an adjoining portion ofthe groove wall. If this transition region has an angled configuration,the angle between the adjoining portion of the groove wall and the wallof the recess, as seen from the inside of the cathode block, ispreferably 90 degrees to 160 degrees, particularly preferably 90 degreesto 135 degrees and very particularly preferably 100 degrees to 120degrees. If this transition region has a curved configuration, possiblybut not necessarily ideally a configuration curved like a circle, theradius of curvature of the transition region is preferably at most 50mm, particularly preferably at most 20 mm and most preferably at most 5mm.

According to a further preferred embodiment of the present invention,the wall which delimits the groove comprises a bottom wall and two sidewalls, each side wall having at least one recess, preferably a recesswhich extends perpendicularly to the surface of the respective sidewall. In this way, the busbar is held on both sides in the groove, as aresult of which the busbar can be fixed particularly effectively in thedesired position. In principle, it is also possible for a plurality ofrecesses to be provided in one or in both of the side walls, for exampleat least 1, at least 2, at least 3 or at least 4 recesses per side wall,into each of which the encasement of the busbar of cast iron engages atleast in certain portions. A particularly strong connection between thebusbar and the cathode block is achieved as a result. It is preferablefor the depth and/or the volume of the individual recesses to be all themore lower as more recesses are provided in the groove.

It is preferable for the at least one recess to be at an at leastsubstantially constant distance from the bottom wall of the groove overits length and to run parallel thereto. In such a configuration,displaceability of the busbar parallel to the groove bottom is ensured.

According to a further preferred embodiment of the present invention,each of the at least one recess is lined at least in certain regions andpreferably over its full extent with the graphite foil, in which case itgoes without saying that the remaining regions of the groove are alsopreferably lined over their full extent with the graphite foil. As aconsequence, a particularly low electrical contact resistance betweenthe cast iron and the cathode block is produced even in the region ofthe recesses. In addition, the sliding properties of the graphite foilmean that it is possible to ensure displaceability of the busbar, asdescribed above, in the longitudinal direction of the at least onerecess and therefore in the longitudinal direction of the cathode block,if the majority of the surface and preferably at least approximately theentire surface of the wall which delimits the groove is lined withgraphite foil. In this case, the graphite foil can be pressed againstthe boundary of the recess by the encasement of the busbar of cast iron,in order to bring about both particularly good electrical contact andalso a particularly effective positive fit. This effect becomesimportant especially during heating of the electrolysis cell for startup, since the specific thermal expansion of steel or iron isapproximately three times the specific thermal expansion of conventionalcathode materials.

The at least one recess of the groove can be lined with the graphitefoil during the production of the cathode configuration simply byinserting the graphite foil into the groove such that it fills therecess, and then pouring the cast iron into the groove in such a mannerthat the graphite foil is pressed into the recess, where it is pressedin particular directly against the cathode block material which delimitsthe recess.

In order to achieve a vertical current density distribution which isuniform over the cathode block length, it is proposed in a developmentof the concept of the invention that the at least one groove has a depthwhich varies over its length or the length of the cathode block, itbeing particularly preferable for the center of the groove, with respectto the longitudinal direction, to have a greater depth than the twolongitudinal-side ends thereof. This achieves a uniform distribution ofthe electric current fed via the cathode configuration over the entirelength of the cathode block, as a result of which an excessive electriccurrent density at the longitudinal-side ends of the cathode block andthus premature wear at the ends of the cathode block is avoided. In thisembodiment, virtually the only applicable cross-sectional form for thegroove is rectangular, and therefore the effect of the presentinvention, specifically that of reliably avoiding falling out of thebusbar from the groove opening, is particularly pronounced here.

Such a uniform current density distribution over the length of thecathode block avoids movements in the aluminum melt which are caused bythe interaction of electromagnetic fields, and it is thereby possible toarrange the anode at a smaller height above the surface of the aluminummelt. This reduces the electrical resistance between the anode and thealuminum melt and increases the energy efficiency of the fused-saltelectrolysis which is carried out.

In the above-described embodiment, too, in which the cathode block has agroove of variable depth, the at least one recess of the cathode blockis preferably configured such that it is at a substantially constantdistance from the bottom of the groove over the length of the groove, inorder to thereby make it possible to displace the busbar as requiredalong the longitudinal direction of the cathode block.

The cathode configuration according to the invention is also suitablewithout any problems in particular for the use of conventional grooveand/or busbar geometries. By way of example, the groove and/or thebusbar can conventionally have a substantially rectangular crosssection. This is preferable in particular if the groove has a depthwhich varies in the longitudinal direction. The busbar, in particular,can also conventionally consist of steel.

In a development of the concept of the invention, it is proposed thatthe graphite foil lining the groove at least in certain regions containsexpanded graphite and particularly preferably compressed expandedgraphite, which is particularly preferably free of binders. It is veryparticularly preferable for the graphite foil lining the groove at leastin certain regions to consist of expanded graphite and particularlypreferably of compressed expanded graphite free of binders. As set forthabove, the foil in principle can also be formed by a substantiallyplate-shaped blank, which contains expanded graphite and in this casehas a sufficient elasticity to be deformed elastically such that itpermits the above-described filling of the recess by the cast ironencasement and in the process can be inserted into the recess betweenthe cast iron and the wall which delimits the groove.

The graphite content of the graphite foil is preferably at least 60%,further preferably at least 70%, particularly preferably at least 80%,especially preferably at least 90% and very particularly preferably atleast approximately 100%.

Good results in terms of optimum exploitation of the mechanical andelectrical properties of the graphite are achieved in particular if thegraphite foil has a thickness of between 0.2 mm and 3 mm, preferablybetween 0.2 mm and 1 mm and particularly preferably between 0.3 mm and0.5 mm.

Depending on the desired properties, the graphite foil can be insertedor adhesively bonded into the groove. Adhesive bonding of the graphitefoil into the groove is preferable in particular if the graphite foil ispressed to only a relatively small degree against the surface of therecess, or if displacement of the graphite foil, no matter how small, inthe longitudinal direction of the cathode block is to be avoided.

According to a further preferred embodiment of the present invention,the cathode block has one or two grooves for receiving in each case atleast one busbar. In principle, it is possible within the context of theinvention for one groove of the cathode block to receive exactly onebusbar, but in particular also two busbars, which are inserted intovarious portions of the length of the groove. In this case, the busbarscan be arranged so that they lie opposite one another on their faces.

The present invention also relates to a cathode block for a cathodeconfiguration of an aluminum electrolysis cell based on carbon and/orgraphite, which has at least one groove for receiving a busbar, whereinat least one recess is provided in the wall of the cathode block whichdelimits the at least one groove. Such a cathode block canadvantageously be used as a component part of the cathode configurationdescribed above. Here, the cathode block can be constructed on the basisof amorphous carbon, graphitic carbon, graphitized carbon or any desiredmixture of the above carbons.

The present invention also relates to a process for producing a cathodeconfiguration for an aluminum electrolysis cell, comprising thefollowing steps:

providing a cathode block based on carbon and/or graphite, which has atleast one groove for receiving a busbar, wherein at least one recess isprovided in the wall of the cathode block which delimits the at leastone groove,

lining at least a region of the at least one groove with a graphitefoil,

inserting a busbar into the at least one groove,

pouring liquid cast iron into at least a portion of the at least onerecess between the graphite foil and the busbar, and

allowing the cast iron to solidify.

The static pressure of the cast iron column thrusts the graphite foillocated in the groove into the at least one recess, where it is pressedin particular against the cathode block which delimits the at least onerecess. It is thereby possible with particular ease to produce a cathodeconfiguration having a recess lined partially or completely by thegraphite foil which has a particularly low electrical contact resistancebetween the busbar and the cathode block. During heating of theelectrolysis cell for start up, particularly close contact is achievedby the different thermal expansions of steel or iron and the cathodematerial.

The graphite foil can be inserted and/or adhesively bonded into thegroove before the busbar is inserted. A loose insertion of the graphitefoil in the groove can be sufficient as a prefixing, since the graphitefoil is preferably pressed by the cast iron against the at least onewall of the cathode block which delimits the groove during casting.

For producing the cathode block, a carbon-containing orgraphite-containing starting material or a mixture of a plurality ofsuch materials can be brought into a mold and then compacted to form agreen body. The starting materials in this case are preferably presentin particulate or granular form. Then, the green body can be heated andthus carbonized and, if appropriate, graphitized. Within the context ofthe present invention, it is possible to use both carbonized cathodeblocks, which are understood to mean those cathode blocks which, duringtheir production, have been subjected to heat treatment of up to at most1500° C. and preferably between 800 and 1200° C. and have a high contentof amorphous carbon, and also graphitized cathode blocks, which areunderstood to mean those cathode blocks which, during their production,have been subjected to heat treatment of more than 2000° C. andpreferably between 2300 and 2700° C. and have a high content ofgraphite-like carbon. Finally, it is possible to use cathode blocksbased on graphitic carbon, i.e. those which have not been graphitizedbut to which graphite has been added as starting material.

As the starting substances for carbonized cathode blocks, use is madefor example of a mixture of calcined anthracite, graphite and coal tarpitch and/or petroleum pitch, whereas graphitic cathode blocks areproduced for example from a mixture containing graphite and coal tarpitch and/or petroleum pitch. Here, graphite denotes both natural andsynthetic graphite.

According to an advantageous development of the process, during theproduction of the cathode block, the starting material containing carbonand/or graphite is introduced into a mold, which has a protrusion formedcomplementarily to the at least one recess.

Similarly, the at least one recess can be produced by subsequentlyremoving and/or eliminating cathode block material of the at least onewall of the cathode block which delimits the groove. It is possible inparticular for the recess to be introduced subsequently by a millingprocess, in which case a milling head used for introducing the recesspreferably has a cross section corresponding to the recess.

The present invention also relates to a cathode configuration that maybe obtained by way of the above-described process.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a cathode configuration and cathode block with a groove having aguide recess, it is nevertheless not intended to be limited to thedetails shown, since various modifications and structural changes may bemade therein without departing from the spirit of the invention andwithin the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a cross section of a detail of an aluminum electrolysiscell having a cathode configuration according to an exemplary embodimentof the present invention;

FIG. 2 shows a longitudinal section of the cathode configuration of thealuminum electrolysis cell shown in FIG. 1; and

FIGS. 3A-3D show exemplary cross sections of recesses which are providedin a groove of a cathode block according to the invention.

DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a cross section of adetail of an aluminum electrolysis cell 10 having a cathodeconfiguration 12, which at the same time forms the bottom of a tank foran aluminum melt 14 produced during operation of the electrolysis cell10 and for a cryolite-aluminum oxide melt 16 located above the aluminummelt 14. An anode 18 is in contact with the cryolite-aluminum oxide melt16. At the side, the tank formed by the lower part of the aluminumelectrolysis cell 10 is delimited by a carbon and/or graphite lining(not shown in FIG. 1).

The cathode configuration 12 comprises a plurality of cathode blocks 20,which are each connected to one another via a ramming mass 24 which hasbeen inserted into a ramming mass joint 22 arranged between the cathodeblocks 20. A cathode block 20 in this case comprises two grooves 26arranged on the underside thereof, having a rectangular, specifically asubstantially rectangular cross section, wherein a busbar 28 of steellikewise having a rectangular cross section is received in each groove26. Here, each wall 32, 34 delimiting the groove 26 is lined by agraphite foil 30, which is indicated by dashed lines in FIG. 1.

The grooves 26 are each delimited by two side walls 32 and a bottom wall34 of the cathode block 20, with a recess 36 extending substantiallyperpendicularly into the side wall 32 and having an approximatelysemicircular cross section being provided in each of the side walls 32.Each recess 36 is delimited by an upper and a lower transition region 37of the cathode block 20. In the present exemplary embodiment, thetransition regions 37 have an angled configuration, with an angle αbetween the adjoining portion of the groove wall and the wall of therecess of 90 degrees. In this case, the interstice between the busbar 28and the groove 26 lined with the graphite foil 30 is poured out in eachcase with cast iron 38, and therefore the graphite foil 30 is fixedbetween the cast iron 38 and the cathode block 20. In this case, thegraphite foil 30 is pressed against the walls 32, 34 which delimit therespective groove 26 by the cast iron 38. In the present exemplaryembodiment, the recesses 36 are also each lined by the graphite foil 30,in which case the cast iron 38 positively fills the lined recesses 36and presses the graphite foil 30 against the cathode block 20 whichdelimits the recess 36. In this way, a low electrical contact resistancebetween the busbar 28 and the cathode block 20 is ensured over theentire cross section of the groove 26. The cast iron 38 forms anencasement 39 for the busbar 28 and is integrally connected to thebusbar 28.

In addition, the cast iron 38 received in the recesses 36 in each caseforms a positively-locking connection with the material of the cathodeblock 20 which delimits the recess 36, and this prevents movement of thebusbar 28 connected to the cast iron 38 in the direction of the arrow40. This prevents undesirable movement of the busbar 28 in the depthdirection of the groove 26 or prevents even the busbar 28 from fallingout of the groove 26. In this context, a positively locking connectionis also referred to as a form-lock, as opposed to a friction lock orforce lock.

FIG. 1 specifically shows the cross section of the cathode configuration10 at a longitudinal-side end of the cathode block 20. In this case, thedepth of the grooves 26 of the cathode block 20 varies over the lengthof the grooves 26. The groove cross section in the region of the centerof the groove 26 is indicated by a dashed line 42 in FIG. 1. In thepresent exemplary embodiment, the difference between the groove depth atthe longitudinal-side ends of the groove 26 and in the center of thegroove 26 is approximately 10 cm. The width 44 of each groove 26 issubstantially constant over the entire groove length and isapproximately 15 cm, whereas the width 46 of each of the cathode blocks20 is approximately 65 cm.

In the present exemplary embodiment, a plurality of anodes 18 and aplurality of cathode blocks 20 are arranged one above the other in sucha way that each anode 18 covers two cathode blocks 20 arranged alongsideone another in width and covers half a cathode block 20 in length. Ineach case, two anodes 18 that are arranged alongside one another coverthe length of a cathode block 20.

FIG. 2 is a longitudinal section showing the cathode block 20 shown inFIG. 1. As can be seen from FIG. 2, the groove 26, considered in itslongitudinal section, tapers towards the center of the cathode block 20in the form of a triangle, as a result of which a substantially uniformvertical electric current density is ensured over the entire cathodelength. As indicated by a dashed line in FIG. 2, the recesses 36 hererun parallel to the groove bottom 34 and are at a constant distance fromthe groove bottom 34 over the length of the groove 26. In the presentexemplary embodiment, the busbar 28, which is not shown in FIG. 2 forthe sake of greater clarity, has a bar-like form and has a rectangularlongitudinal section, such as to form an interstice between the busbarand the groove bottom 34, which interstice increases in size towards thecenter of the groove 26 and can be filled either by cast iron 38 or byadditional metal plates connected to the busbar 28. Similarly, it wouldalso be possible to use a busbar 28 which is matched in its longitudinalsection to the triangular profile of the groove 26.

Finally, FIGS. 3A to 3D show exemplary recesses 36, which are providedin a groove of a cathode block 20 according to the invention, in crosssection. Here, the recesses 36 each have a substantially semicircularcross section (FIG. 3A), a substantially trapezoidal cross section (FIG.3B) or a substantially triangular cross section (FIG. 3C). The angle αof the transition regions 37 between the wall of the recess 36 and theadjoining portion of the groove wall 32, as seen from the inside of thecathode block 20, is in this case about 90° in FIG. 3A, about 120° inFIG. 3B and about 125° in FIG. 3C. FIG. 3D shows a configuration inwhich a plurality of recesses 36, each with a triangular cross sectionas in FIG. 3C, are formed in succession in the depth direction of thegroove 26, in order to particularly reliably hold an inserted busbar 28.In this case, the transition regions 48 between two adjoining recesses36 have an angle β of about 70° between the walls of two adjoiningrecesses 36, as seen from the inside of the cathode block 20. Therecesses 36 shown in FIGS. 3A to 3 d each extend perpendicularly intothe side wall 32 of the cathode block 20 which delimits the groove 26,such that they form a fixing with cast iron received in the recesses 36,which is effective in the depth direction of the groove 26 and preventsundesirable movement of the busbar 28 parallel to the depth direction ofthe groove 26 after the busbar 28 has been cast with cast iron 38.

The following is a list of reference symbols used in the abovedescription of the drawing figures:

-   10 Aluminum electrolysis cell-   12 Cathode configuration-   14 Aluminum melt-   16 Cryolite-aluminum oxide melt-   18 Anode-   20 Cathode block-   22 Ramming mass joint-   24 Ramming mass-   26 Groove-   28 Busbar-   30 Graphite foil-   32 Side wall-   34 Bottom wall-   36 Recess-   37 Transition region between the wall of the recess and the    adjoining portion of the groove wall-   38 Cast iron-   39 Encasement-   40 Arrow-   42 Dashed line-   44 Width of the groove 26-   46 Width of the cathode block 20-   48 Transition region between two adjoining recesses-   α Angle between the wall of the recess and the adjoining portion of    the groove wall-   β Angle between the walls of two adjoining recesses

1. A cathode configuration for an aluminum electrolysis cell, thecathode configuration comprising: at least one cathode block based on atleast one material selected from the group consisting of carbon andgraphite; said at least one cathode block having a groove formed thereinlined with a graphite foil at least in certain regions thereof; a wallof said cathode block delimiting said groove having at least one recessformed therein; a busbar disposed in said groove, said busbar having anencasement of cast iron at least in certain regions thereof, saidencasement of cast iron engaging into said at least one recess in saidgroove at least in certain portions thereof.
 2. The cathodeconfiguration according to claim 1, wherein a portion of said encasementof cast iron engaging into said at least one recess is formed in acomplementary shape to said recess.
 3. The cathode configurationaccording to claim 1, wherein a portion of said encasement engaging intosaid at least one recess and, if appropriate, said busbar encasedthereby fill at least 70% of the recess.
 4. The cathode configurationaccording to claim 1, wherein said at least one recess extendscontinuously over at least 20% of a length of said groove.
 5. Thecathode configuration according to claim 1, wherein said at least onerecess has a depth of 2 mm to 40 mm.
 6. The cathode configurationaccording to claim 1, wherein said at least one recess has an openingwidth, based on a height of said cathode block, of 2 mm to 40 mm.
 7. Thecathode configuration according to claim 1, wherein said at least onerecess has a cross-sectional shape selected from the group consisting ofsubstantially semicircular, triangular, rectangular and trapezoidal. 8.The cathode configuration according to claim 1, wherein said recessextends substantially perpendicularly into the wall of said cathodeblock delimiting said groove.
 9. The cathode configuration according toclaim 1, wherein, considered in a depth direction of said groove, saidat least one recess is delimited at each end thereof by a transitionregion between said recess and an adjoining portion of the groove wall,wherein each of said transition regions has an angled configuration,wherein an angle between said wall of said recess and an adjoiningportion of the groove wall, as seen from the inside said cathode block,amounts to between 90° and 160°.
 10. The cathode configuration accordingto claim 1, wherein, considered in a depth direction of said groove,said at least one recess is delimited at each end thereof by atransition region between said recess and an adjoining portion of thegroove wall, wherein each of said transition regions has a curvedconfiguration, wherein the radius of curvature of the transition regionis at most 50 mm.
 11. The cathode configuration according to claim 1,wherein said wall delimiting said groove is formed with a bottom walland two side walls, and wherein each of said side walls is formed with arespective said recess.
 12. The cathode configuration according to claim1, wherein said at least one recess is formed at a substantiallyconstant spacing distance from a bottom wall of said groove over alength of said recess.
 13. The cathode configuration according to claim1, wherein said at least one recess is lined with said graphite foil,and said groove is lined over a full extent thereof with said graphitefoil.
 14. The cathode configuration according to claim 13, wherein saidgraphite foil is pressed against a boundary of said recess by saidencasement of said busbar formed of cast iron.
 15. The cathodeconfiguration according to claim 1, wherein said groove has a variabledepth over a length thereof.
 16. The cathode configuration according toclaim 15, wherein longitudinal-side ends of said groove have a lesserdepth than a center of said groove.
 17. The cathode configurationaccording to claim 1, wherein said graphite foil is inserted and/oradhesively bonded into the groove.
 18. A cathode block for a cathodeconfiguration of an aluminum electrolysis cell, comprising: a carbonand/or graphite block having at least one groove formed therein forreceiving a busbar; a wall of said block delimiting said groove havingat least one recess formed therein.
 19. A process for producing acathode configuration for an aluminum electrolysis cell, the methodwhich comprises the following steps: providing a cathode block based onat least one material selected from the group consisting carbon andgraphite and formed with at least one groove for receiving a busbar, andwith at least one recess formed in a wall of the cathode block thatdelimits the at least one groove; lining at least a region of the atleast one groove with a graphite foil; inserting a busbar into the atleast one groove; pouring liquid cast iron into at least a portion ofthe at least one recess between the graphite foil and the busbar; andallowing the cast iron to solidify.
 20. The process according to claim19, which comprises inserting the graphite foil into the groove and/oradhesively bonding the graphite foil in the groove.